A field effect transistor (FET) is used in a switching power supply device used as an alternating current (AC)/direct current (DC) converter or a DC/DC converter or a semiconductor device such as an amplifier or the like. A silicon (Si)-metal-oxide-semiconductor (MOS) FET, for example, is widely used as the FET. In recent years, a dedicated control integrated circuit (IC) has often been used as a control circuit that performs on-off control of the FET. A gate drive voltage of the Si-MOSFET is 7 to 20 V. The control IC therefore outputs a gate voltage in that range in many cases.
Meanwhile, in recent years, a high electron mobility transistor referred to as a high electron mobility transistor (HEMT) has been developed. As a typical HEMT, there is a GaN-HEMT using a compound semiconductor of gallium nitride (GaN) having a small on-resistance.
Incidentally, a technology is proposed which suppresses an overvoltage on a positive side in a switching power supply device using GaN in a switching element. In addition, a technology is proposed which operates a driving circuit by a power supply of a single polarity.
GaN-HEMTs that may be used in amplifiers are of a normally on type, and many of the GaN-HEMTs adopt a Schottky gate. A gate voltage thereof is therefore negative, and is in a range of −8 to 0 V, for example.
It is difficult for a control IC that assumes the use of a Si-MOSFET to drive a FET for which a negative voltage is used, such as a normally on type GaN-HEMT having the characteristics as described above or the like. A negative power supply may be added to generate the negative voltage. However, a circuit scale is increased.
The followings are reference documents.    [Document 1] Japanese Patent No. 6160762 and    [Document 2] Japanese Laid-open Patent Publication No. 10-232384.